SEATTLE—Law enforcement detained dozens of protesters Monday for trying to block a Royal Dutch Shell RDS.A -0.03 % PLC oil rig from departing the Port of Seattle for drilling off Alaska—the latest development in a weekslong standoff in which environmental activists have been joined by an unusual ally: the city itself. Monday’s action took place after the Polar Pioneer and its support vessels attempted to leave the port about 6 a.m. to begin exploratory drilling in the Chukchi Sea and were intercepted by protesters in kayaks, Coast Guard officials said. About two dozen people were detained, including Seattle City Councilman Mike O’Brien, as more activists prepared to try to block the 400-by-292-foot drilling vessel from reaching the open sea, said Coast Guard Lt. Dana Warr. Lt. Warr said the agency is enforcing a 500-yard safety zone around the vessel, and that violators face misdemeanor citations. Shell officials said that […]